Interbody spinal fusion implant having an anatomically conformed trailing end

ABSTRACT

An interbody spinal fusion implant adapted for placement at least in part across an intervertebral space formed across a disc space between two adjacent vertebral bodies and for penetrating engagement into each of those vertebral bodies, the implant having a trailing end adapted to sit upon and not protrude from the anterolateral peripheral rim of bone of the vertebral body.

RELATED APPLICATION

This is a continuation of application Ser. No. 09/263,266, filed Mar. 5,1999, now U.S. Pat. No. 6,241,770, incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to interbody spinal fusionimplants that are securely placed into the intervertebral space createdacross the spinal disc between two adjacent vertebral bodies after theremoval of damaged spinal disc material and preferably at least somevertebral bone from each of the adjacent vertebral bodies for thepurpose of achieving interbody spinal fusion, which fusion occurspreferably at least in part through the spinal fusion implant itself. Inparticular, the present invention is directed to an improved, interbodyspinal fusion implant having opposed arcuate surfaces for penetrablyengaging each of the vertebral bodies adjacent a disc space in the humanspine and having a trailing end configured to conform to the anatomiccontour of the anterior and/or lateral aspects of the vertebral bodies,so as to not protrude beyond the curved contours thereof, and in onepreferred embodiment of the present invention the above describedimplants are structurally adapted to be rotated for proper insertion.

2. Description of the Related Art

Surgical interbody spinal fusion generally refers to the methods forachieving a bridge of bone tissue in continuity between adjacentvertebral bodies and across the disc space to thereby substantiallyeliminate relative motion between the adjacent vertebral bodies. Theterm “disc space” refers to the space between adjacent vertebraenormally occupied by a spinal disc.

Human vertebral bodies have a hard outer shell of compact bone(sometimes referred to as the cortex) and a relatively softer, innermass of cancellous bone. Just below the cortex adjacent the disc is aregion of bone referred to herein as the “subchondral zone”. The outershell of compact bone (the boney endplate) adjacent to the spinal discand the underlying subchondral zone are together herein referred to asthe boney “end plate region” and, for the purposes of this application,is hereby so defined to avoid ambiguity. A circumferential ring of densebone extends around the perimeter of the endplate region and is themature boney successor of the “apophyseal growth ring”. Thiscircumferential ring comprises of very dense bone and for the purposesof this application will be referred to as the “apophyseal rim”. Thespinal disc that normally resides between the adjacent vertebral bodiesmaintains the spacing between those vertebral bodies and, in a healthyspine, allows for the normal relative motion between the vertebralbodies.

Reference is made throughout this Background section to the attacheddrawings in order to facilitate an understanding of the related art andproblems associated therewith. In FIG. 1, a cross-sectional top planview of a vertebral body V in the lumbar spine is shown to illustratethe dense bone of the apophyseal rim AR present at the perimeter of thevertebral body V about the endplate region and an inner mass ofcancellous bone CB. The structure of the vertebral body has beencompared to a core of wet balsa wood encased in a laminate of white oak.From the top plan view in FIG. 1, it can be seen that the beststructural bone is peripherally disposed.

FIG. 2 is a top plan view of a fourth level lumbar vertebral body Vshown in relationship anteriorly with the aorta and vena cava(collectively referred to as the “great vessels” GV).

FIG. 3 is a top plan view of a fifth lumbar level vertebral body V shownin relationship anteriorly with the iliac arteries and veins referred toby the designation “IA-V”. The location of these fragile blood vesselsalong the anterior aspects of the lumbar vertebrae makes it imperativethat no hardware protrude dangerously therefrom where the vessels couldbe endangered.

Implants for use in human spinal surgery can be made of a variety ofmaterials such as surgical quality metals, ceramics, plastics andplastic composites, cortical bone and other materials suitable for theintended purpose, and further may be absorbable and or bioactive as inbeing osteogenic. Fusion implants preferably have a structure designedto promote fusion of the adjacent vertebrae by allowing bone to growthrough the implant from vertebral body to adjacent vertebral body tothereby fuse the adjacent vertebrae. This type of implant is intended toremain indefinitely within the patient's spine or if made of bone orother resorbable material to eventually be replaced with the patient'sbone.

Michelson, Ray, Bagby, Kuslich, and others have taught the use ofhollow, threaded perforated cylinders to be placed across a disc spacebetween two adjacent vertebrae in the human spine to encourage interbodyspinal fusion by the growth of bone from one vertebra adjacent a disc tothe other vertebra adjacent that disc through such implants. Michelson,Zdeblick and others have also taught the use of similar devices thateither have truncations of their sides such that they are not completecylinders, and/or are tapered along their longitudinal axis much like acylinder which has been split longitudinally and then wedged apart. Allof these implants have in common opposed arcuate surfaces for penetrablyengaging into each of the vertebral bodies adjacent a disc space to befused. Such implants now in common use throughout the spine, may be usedindividually or inserted across the disc space in side-by-side pairs,and may be insertable from a variety of directions.

It is commonly held by surgeons skilled in the art of spinal fusion thatthe ability to achieve spinal fusion is inter alia directly related tothe vascular surface area of contact over which the fusion can occur,the quality and the quantity of the fusion mass (e.g. bone graft), andthe stability of the construct. However, the overall size of interbodyspinal fusion implants is limited by the shape of the implants relativeto the natural anatomy of the human spine. For example, such implantscannot dangerously protrude from the spine where they might cause injuryto one or more of the proximate vital structures including the largeblood vessels.

With reference to FIG. 4, a top plan view of the endplate region of avertebral body V is shown to illustrate the area H available to safelyreceive an implant(s) inserted from the anterior aspect (front) of thespine, with the blood vessels retracted.

As can be seen in FIG. 5, a top plan view of the endplate region of avertebral body V with the outlines of two differentially sized prior artimplants A and B installed, one on each side of the midline of thevertebral body V, are shown. The implantation of such prior art implantsA and B is limited by their configuration and the vascular structurespresent adjacent anteriorly to the implantation space. For example, thegreat vessels GV present at the L₄ level and above are shown in solidline in FIG. 5, and for the L₅ and S₁ levels, the iliac artery and veinIA-V are shown in dotted line. As shown in FIG. 5, prior art implant Arepresents an attempt by the surgeon to optimize the length of theimplant which is inhibited by a limiting corner LC. Implant A, thelongest prior art implant that can be inserted without interfering withthe great vessels GV adjacent the vertebral body V, leaves cross-hatchedarea X of a cross section the vertebral body at the endplate regionwasted which would be a very useful surface for contact for fusion andfor support of the implant by the vertebral body. Similarly, implant Bis an attempt by the surgeon to optimize the width of an implant whichis also inhibited by a limiting corner LC′. Implant B, the widest priorart implant that can be inserted without interfering with the greatvessels GV adjacent the vertebral body V, leaves cross-hatched area Y ofthe cross section of the vertebral body adjacent the endplate regionwasted which could otherwise be a very useful surface area for contactfor fusion and for support of the implant by the vertebral body. Thepresence of limiting corners LC and LC′ on any such implants precludesthe surgeon from safely utilizing an implant having both the optimalwidth and length, that is the length of implant A and the width ofimplant B combined, as such an implant would markedly protrude from thespine and endanger the large blood vessels.

FIG. 5 illustrates the maximum dimensions for the above discussed priorart implants A and B to be safely contained within the spine so that acorner LC or LC′ of the trailing end (side wall to trailing endjunction) or the most rearward extension of that sidewall does notprotrude outward beyond the rounded contour of the anterior (front) orthe anterolateral (front to side) aspect of the vertebral bodies. Priorart implant A maximizes length, but sacrifices width and for the mostpart fails to sit over the best supportive bone peripherally of theapophyseal rim as previously shown in FIG. 1. Prior implant B maximizeswidth, but sacrifices length and again fails to sit over the beststructural bone located peripherally in the apophyseal rim of thevertebral body, comprising of the cortex and dense subchondral bone.Both prior art implants A and B fail to fill the area available with aloss of both vital surface area over which fusion could occur and a lossof the area available to bear the considerable loads present across thespine.

Similarly, FIG. 6A shows the best prior art cross-sectional area fillfor a pair of inserted threaded implants G as per the current prior art.Note the area Y anterior to the implants G, including the excellentstructural bone of the apophyseal rim AR, is left unused, and thusimplants G fail to find the best vertebral support. Since the wastedarea Y anterior to the implants G is three dimensional, it also wastes avolume that optimally could be utilized to hold a greater quantity ofosteogenic material. Finally, the implants of the prior art fail toachieve the optimal stability that could be obtained by utilizing thegreater available surface area of contact and improved length that animplant with the maximum width and length would have, and thereby thebest lever arms to resist rocking and tilting, and increased contactarea to carry further surface protrusions for providing stability byengaging the vertebrae, such as with the example shown of a helicalthread.

FIG. 11 shows the best fill obtained when a prior art implant C isinserted, from a lateral approach to the spine (from a position anteriorto the transverse processes of the vertebrae) referred to herein as the“translateral approach” or “translaterally” across the transverse widthW of vertebral body V. Some examples of implants inserted from thetranslateral approach are the implants disclosed in U.S. Pat. No.5,860,973 to Michelson and preferably inserted with the method disclosedin U.S. Pat. No. 5,772,661 to Michelson. Implant C does not entirelyoccupy the cross-sectional area of the end plate region and leavescross-hatched area Z of the vertebral body V unoccupied by the implantwhich area would be useful for contact for fusion and for support of theimplant. The configuration of the trailing corner LC″ of the prior artimplant C prevents implant C from being sized larger and prevents thefull utilization of the surface area of contact of the vertebral bodycross-sectional area resulting in a sub-optimal fill of the disc spacewith the implant, and little of the implant sitting on the apophysealrim.

The configuration of prior art implants prevents the utilization of theapophyseal rim bone, located at the perimeter of the vertebral body tosupport the implants at their trailing ends. The utilization of thisdense bone would be ideal.

Therefore, there is a need for an interbody spinal fusion implant havingopposed arcuate portions for penetrably engaging adjacent vertebralbodies, including implants requiring rotation for proper insertion intoan intervertebral space formed across the disc space between twoadjacent vertebrae, that is capable of fitting within the externalperimeter of the vertebral bodies between which the implant is to beinserted to maximize the surface area of contact of the implant andvertebral bone without the danger of interfering with the great vesselsadjacent to the vertebrae into which the implant is to be implanted.There exists a further need for an implant that is adapted to utilizethe dense cortical bone in the perimeter of the vertebral bodies insupporting such an implant installed in a disc space.

SUMMARY OF THE INVENTION

The present invention relates to preformed, manufactured interbodyspinal fusion implants for placement between adjacent vertebral bodiesof a human spine at least in part across the disc space between thoseadjacent vertebral bodies, without dangerously extending beyond theouter dimensions of the two adjacent vertebral bodies adjacent that discspace, to maximize the area of contact of the implant with the vertebralbone. For example, the present invention specifically excludes bonegrafts harvested from a patient and shaped by a surgeon at the time ofsurgery such as those of cancellous or corticocancellous bone. Thepresent invention can benefit implants requiring an element of rotationfor proper insertion into the implantation space, and more generally,any and all interbody spinal fusion implants having opposed arcuatesurfaces spaced apart to penetrably engage within the substance of theopposed adjacent vertebral bodies, as opposed to merely contacting thosevertebral bodies at their exposed boney endplates.

In one embodiment of the present invention, an implant for insertionfrom the anterior approach of the spine and for achieving better fillingof the anterior to posterior depth of the disc space between twoadjacent vertebral bodies comprises opposed arcuate portions forpenetrably engaging the bone of the adjacent vertebral bodies deep intothe boney endplate, a leading end which is inserted first into the discspace, and an opposite trailing end. The trailing end of this embodimentof the implant of the present invention is generally configured toconform to the natural anatomical curvature of the perimeter of theanterior aspect of vertebral bodies, such that when the implant is fullyinserted and properly seated within and across the disc space, thesurface area of the vertebral bone in contact with the implant ismaximized safely. Moreover, the implant of the present invention is ableto seat upon the dense compacted bone in the perimeter of the vertebralbodies for supporting the load through the implant when installed in theintervertebral space.

More specifically, in the present invention, while the implant overallmay be enlarged relative to the sizes possible with prior implants, thelimiting corner of the trailing end and side wall at the trailing endhas been removed. It has been the need in the past to keep this limitingcorner of the implant from protruding beyond the perimeter of the discspace that has prevented these same implants from being of the optimalsize overall so as to maximize the area of contact and to seat upon andbe supported by the peripheral rim of densely compacted bone.

As another example, for an implant to be inserted from the lateralaspect of the spine, the implant of the present invention has opposedarcuate surfaces for penetrably engaging each of the vertebral bodiesadjacent the disc space to be fused, a leading end which is insertedfirst into the disc space, and an opposite trailing end. The trailingend is configured to conform to the curvature of the lateral aspect ofthe perimeter of the vertebral bodies adjacent the disc space andwithout dangerously extending beyond the outer dimensions of the twovertebral bodies, such that when the implant is inserted in the discspace, the surface area of the vertebral bone in contact with theimplant is maximized without interfering with any of the vitalstructures adjacent to those vertebral bodies.

The spinal implants of the present invention may also have at least oneopening allowing for communication between the opposed upper and lowervertebrae engaging surfaces to permit for bone growth in continuitythrough the implant from the adjacent vertebral bodies for fusion acrossthe disc space of the adjacent vertebral bodies, and through theimplant.

For any of the embodiments of the present invention described herein,the implants may include protrusions or surface roughenings for engagingthe bone of the vertebral bodies adjacent to the implant. The materialof the implant may be an artificial material such as titanium or one ofits implant quality alloys, cobalt chrome, tantalum, or any other metalappropriate for surgical implantation and use as an interbody spinalfusion implant, or ceramic, or composite including various plastics,carbon fiber composites, and can include materials which are at least inpart bioresorbable. The materials of the implant also can includetransplants of cortical bone or other naturally occurring materials suchas coral, and the implants may further comprise osteogenic materialssuch as bone morphogenetic proteins, or other chemical compounds, thepurpose of which is to induce or otherwise encourage the formation ofbone, or fusion, including genetic material coding for production ofbone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a horizontal cross-section through a boneyendplate region of a vertebral body.

FIGS. 2-3 are top plan views of the fourth and fifth level lumbarvertebral bodies in relationship to the blood vessels located anteriorlythereto.

FIG. 4 is a top plan view of an endplate region of a vertebral bodyillustrating the area available to safely receive an implant(s) insertedfrom the anterior aspect of the spine and the area of the annulus thattypically remains from an implantation from an anterior approach.

FIG. 5 is a top plan view of a lumbar vertebral body depicting the safearea of insertion for variously proportioned prior art implants forplacement to either side of the midline.

FIG. 6A is a top plan view of the endplate region of a vertebral bodydepicting the best fit for two threaded spinal implants of the prior artimplanted on either side of the midline.

FIG. 6B is a top plan view of the endplate region of the vertebral bodyshown in FIG. 6A illustrating the optimal proportions and shape of anembodiment of an implant in accordance with the present invention.

FIG. 6C is a top plan view of the endplate region of the vertebral bodyshown in FIG. 6A and two threaded spinal fusion implants of the presentinvention depicting the optimal proportions and shape for such interbodyfusion implants.

FIG. 7A a top plan view of threaded spinal fusion implant of the presentinvention with a driver instrument for engaging the trailing end of theimplant.

FIG. 7B is cross-sectional view along lines 7B-7B of FIG. 7A.

FIG. 7C is a cross sectional view of an implant having one flattenedside in accordance with the embodiment of the present invention.

FIG. 7D is a cross sectional view of an implant having a pair offlattened sides in accordance with an embodiment of the presentinvention.

FIG. 7E is a side elevational view of an implant having opposed portionsthat are generally in a converging relationship to each other from atrailing end to a leading end of the implant in accordance with anembodiment of the present invention.

FIG. 7F is a side elevational view of an implant having opposed portionsthat are generally in a diverging relationship to each other from atrailing end to a leading end of the implant in accordance with anembodiment of the present invention.

FIG. 8 is a front elevational view of two adjacent vertebral bodies withthe outline of another embodiment of the implant of the presentinvention inserted centrally from an anterior approach to the spine.

FIG. 9 is a top plan view of the endplate region of a vertebral body andimplant along line 9-9 of FIG. 8.

FIG. 10 is a top plan view of the endplate region of a vertebral bodywith the outlines of two implants in accordance with another embodimentof the present invention implanted to either side of the midline.

FIG. 11 is a top plan view of the endplate region of a vertebral bodywith a prior art implant implanted translaterally across the transversewidth of the vertebral body from a lateral aspect of the spine.

FIG. 12A is a top plan view of the endplate region of the vertebral bodyof FIG. 11 with an implant of the present invention implantedtranslaterally across the transverse width of the vertebral body from alateral aspect of the spine.

FIG. 12B is a top plan view of the endplate region of the vertebral bodyof FIG. 11 with an alternative embodiment of implants of the presentinvention implanted translaterally across the transverse width of thevertebral body from a lateral aspect of the spine, with the gap betweenthe implants exaggerated for visual effect.

FIG. 12C is a trailing end view of a first of the implants shown in FIG.12B.

FIG. 12D is a leading end view of a second of the implants shown in FIG.12B.

FIG. 13A is a side elevational view of two adjacent vertebral bodieswith two implants of another embodiment of the present inventionimplanted translaterally side-by-side across the transverse width of thevertebrae from a lateral aspect of the spine.

FIG. 13B is a top plan view of the endplate region of a vertebral bodyalong lines 13B-13B of FIG. 13A.

FIG. 14A is a side elevational view of two adjacent vertebral bodieswith two implants of another embodiment of the present inventionimplanted translaterally across the transverse width of the vertebralfrom a lateral aspect of the spine.

FIG. 14B is a top plan view of the endplate region of a vertebral bodyalong line 14B-4B of FIG. 14A.

FIGS. 15A and 15B are top plan views of alternative embodiments of theimplant of the present invention illustrated in outline form.

FIG. 16A is a top view of an alternative embodiment of the implant ofthe present invention illustrated in outline form.

FIG. 16B is a side elevational view of the implants of FIGS. 15A, 15B,and 16A from long side “L”.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 6B shows in outline form the optimal area available to be occupiedby one fusion implant 100 to be inserted into the intervertebral spacein side by side pairs.

With reference to FIGS. 6C, 7A, and 7B, a first embodiment of thepresent invention comprising an interbody spinal implant generallyreferred by the numeral 100, is shown inserted from the anterior aspectof a vertebral body V to each side of the midline M in the lumbar spine.In one embodiment of the present invention, implant 100 has a leadingend 102 for insertion into the disc space, an opposite trailing end 104configured to generally conform to at least a portion of the naturalanatomical curvature of the anterior aspect of the vertebral bodiesadjacent the disc space, and more narrowly to be foreshortened at thataspect of the implant trailing end, that would be most lateral withinthe disc space when implanted within the spine. Implant 100 has opposedarcuate portions 106 and 108 that are oriented toward and adapted topenetrably engage within the adjacent vertebral bodies when insertedacross the intervertebral space. Opposed arcuate portions 106 and 108have a distance therebetween defining an implant height greater than theheight of the disc space at implantation. Preferably, each of theopposed arcuate portions 106 and 108 have at least one opening 110 incommunication with one another to permit for the growth of bone incontinuity from the adjacent vertebral bodies and through implant 100,and as herein shown implant 100 may further be hollow or at least inpart hollow. Implant 100 may also include surface roughening such asthread 120 for penetrably engaging the bone of the adjacent vertebralbodies.

As a result of its configuration, when implant 100 is inserted betweentwo adjacent vertebral bodies, implant 100 is contained within thevertebral bodies and does not dangerously protrude from the spine.Specifically, the most lateral aspect of the implanted implant at thetrailing end has been relieved, foreshortened, or contoured so as toallow the remainder of the implant to be safely enlarged so as to belarger overall than the prior art implants without the trailing endlateral wall protruding from the disc space so as to endanger theadjacent blood vessels (though overall enlargement is not a requisiteelement of the invention).

The present invention is not limited to use in the lumbar spine and isuseful throughout the spine. In regard to use in the cervical spine, byway of example, in addition to various blood vessels the esophagus andtrachea would also be at risk.

Further, the present invention includes such implants having opposedarcuate surface portions as just described whether said opposed portionsare generally parallel along the length of the implant or in angularrelationship to each other such that the opposed arcuate surfaces arecloser to each other proximate one end of the implant than at thelongitudinally opposite other end, or allowing for a variable surface,or any other configuration and relationship of the opposed arcuatesurfaces.

As shown in FIG. 6C, two implants 100 are implanted into theintervertebral space side-by side. The implants 100 of the presentinvention optimally fill the available area and optimally sit on theanterior apophyseal rim. It can be seen that in one embodiment of theimplant 100 of the present invention, trailing end 104 is arcuate to bein conformation to the peripheral profile of the anterior aspect of thevertebral bodies where the implant is in contact with the vertebralbodies so as to allow the implant to have both a maximum safe width andlength, and to sit on the peripheral vertebral body rim, including theanterior cortex and/or the apophyseal rim. This allows the implants ofthe present invention to have the maximum surface area of contact withthe vertebrae, the greatest volume for holding osteogenic material, tosit upon the very good structural bone present at the periphery of thevertebral bodies, to have a greater surface over which to have boneengaging surface irregularities, and as a result of this combination tohave the greatest stability of the implant itself and in turn tostabilize the vertebrae relative to each other.

As shown in FIG. 7A, trailing end 104 may be configured to complementaryengage an instrument 130 for driving implant 100 into the installationspace. Instrument 130 may have a centrally disposed projection 132 andan off-center projection 134 for engaging recesses 142 and 144 oftrailing end 104, respectively. Projection 132 is preferably threaded asis recess 142.

While the implants of FIGS. 6C, 7A, and 7B are shown as cylindrical, theimplant of the present invention includes the novel teaching as appliedto any implants having opposed, at least in part, arcuate surfaces forpenetrably engaging into the vertebral bodies adjacent the disc spaceacross which the implant is implanted for the purpose of achievingfusion. These implants may have flattened or modified sides to be lesswide, such as shown in FIGS. 7C and 7D. Some examples of such implantsare taught by Michelson in U.S. Pat. Nos. 5,593,409 and 5,559,909, andco-pending application Ser. Nos. 08/408,908 and 08/408,928, all of whichare incorporated herein by reference. With reference to FIGS. 8 and 9,when such a teaching is applied for use with a solitary, centrallyplaced implant 200 to be implanted anteriorly and generally along themidline of the disc space, the trailing end 204 of implant 200 would bearcuate as shown, such that trailing end 204 is not rotationallysymmetrical about the mid-longitudinal axis MLA of implant 200, thetrailing end 204 might, in a preferred embodiment, for such use besymmetrical left and right of the mid-longitudinal axis MLA whenproperly inserted alternatively, though not preferred, the implant 200of FIG. 9 for implantation anteriorly could have a rotationallysymmetrical, or even a rounded trailing end.

With reference to FIG. 10, while not achieving the maximum advantage ofthe present inventive teaching, implants 300 a and 300 b (shown inoutlined form) may be used in side by side pairs, each beingsymmetrically arcuate left and right, but not rotationally, about themid-longitudinal axis MLA to provide the advantage that there need notbe mirror image implants or oppositely threaded (left and right)implants provided, and such implants if requiring continuing rotationfor their insertion (designed to be screwed in) can be properly situatedby half turns rather than full turns. That is, the correct alignment ofthe implant occurs every 180° of rotation.

FIG. 10 further shows the area available to safely be filled and thesilhouette of a pair of implants 300 a and 300 b having symmetricallyextended trailing ends 304 a and 304 b for allowing for improved fillingof the disc space and having relieved trailing end to side walljunctions to avoid the implant from protruding dangerously from the discspace anterolaterally. While the fill is not quite as good as with thefully asymmetric trailing end embodiment, the implants of FIG. 10 wheninserted by rotation can be positioned by half-turn increments and theneed for different left and right implants has been eliminated.

As shown in FIG. 11, the best fill relative to a vertebral bodyachievable by prior art implant C disposed anterolaterally across thetransverse width of the vertebral body is limited by corner LC″ andleaves cross-hatched area Z unoccupied by implant C.

With reference to FIG. 12A, another embodiment of the implant of thepresent invention referred to by the numeral 400 is shown. Implant 400is for insertion from the anterolateral aspect of the vertebral body andFIG. 12A illustrates the greatly improved best fill made possible withimplant 400. Implant 400 has a general configuration as described inU.S. Pat. No. 5,860,973 to Michelson, and has a trailing end 404 that isarcuate to generally conform to at least a portion of the naturalanatomical curvature of the lateral aspect of the vertebral bodies. Itis appreciated that implant 400 may include the features of implant 100described above and trailing end 404 may be arcuate, symmetrically orasymmetrically (left and right), about the mid-longitudinal axis MLA ofimplant 400. In this manner, the area Z illustrated in FIG. 11 isoccupied and utilized by implant 400 which can actually be not onlylonger overall, but also wider, or of a larger diameter, as the limitingcorner LC″ of the prior art implant and FIG. 11 has been removed. Asevident from the drawings, the present invention moves the limitingcorner LC formed by the junction of the side wall to the trailing wallor the most rearwardly protruding aspect of the laterally placedsidewall inward away from escaping the disc space.

FIG. 12B is a top plan view of the endplate region of the vertebral bodyof FIG. 11 with an alternative embodiment of first and second implants450 a and 450 b of the present invention implanted translaterally acrossthe transverse width of the vertebral body from a lateral aspect of thespine. Implants 450 a and 450 b are configured such that when they areinstalled, they have a general configuration similar to a single implant400 described above. Typically, implant 450 a is inserted into theimplantation space first, and then implant 450 b is inserted into thesame implantation space behind, and preferably coaxial to, implant 450 ain a “box car” arrangement.

As shown in FIGS. 12C and 12D, trailing end 454 a of implant 450 a isconfigured to be placed in contact with leading end 452 b of implant 450b, and preferably complementary engage leading end 452 b. For example,trailing end 454 a may include raised portions 460 a and 462 a thatcooperatively engage raised portions 460 b and 462 b of leading end 452b of implant 450 b. When implants 450 a and 450 b are in contact, it ispossible to impart movement of implant 450 a within the implantationspace by movement of implant 450 b. In this manner, it is possible tofine tune the depth of insertion of implant 450 a without removingimplant 450 b. The ability to move implant 450 a in this manner alsoprevents stripping of implant 450 b due to the failure of movement ofimplant 450 a.

Implant 450 b can have a trailing end with a conventional configurationor it can have a trailing end 454 b that is arcuate to generally conformto at least a portion of the natural anatomical curvature of the lateralaspect of the vertebral bodies. It is appreciated that implant 450 b mayinclude the features of implant 100 described above and trailing end 454b may be arcuate, symmetrically or asymmetrically (left and right),about the mid-longitudinal axis MLA of implant 450 b. Leading end 452 bmay include a removable end cap 470 with a hex drive 472.

Trailing end 454 a of implant 450 a is preferably flat or indentedconcavely and may include a threaded opening 480 and a slot 482 forengaging insertion instrumentation for driving the implants. The leadingend 452 b of implant 450 b may be flat, preferably with a bevel,chamfer, or radius, or convex to fit into the trailing end 454 a ofimplant 450 a. The radius of the leading flat edge of leading end 452 bof implant 450 b allows implant 450 b to thread into an already tappedpath created by the insertion of implant 450 a and permits the externalthread of implants 450 a and 450 b to functionally align easily.

FIGS. 13A and 13B demonstrate a pair of implants 500 a and 500 b of thepresent invention being used in a side-by-side relationship insertedgenerally laterally or anterolaterally into the spine. As shown in FIGS.14A and 14B, two implants 600 a and 600 b, one anterior, one posterior,the anterior one may be of a larger diameter than the posterior one. Theposterior one may be longer than the anterior one. Each may have atrailing end that is curved from side to side symmetrically orasymmetrically.

The prior art threaded implants, be they for rotation for screwing themin or for less than a full turn rotation for locking them in after theyhave already been linearly advanced into the spine, have all hadgenerally straight trailing ends or trailing ends that have beenrotationally symmetrical in regard to length. In contradistinction, theimplants of the present invention in the preferred embodiment havetrailing ends that are either arcuate or truncated to generally conformto the anterior and/or lateral (anterolateral) peripheral contours ofthe vertebral bodies to be fused at their trailing ends and arespecifically for insertion from the anterior and anterolateral aspectsof the spine and from a position anterior to the transverse processes ofthe vertebrae to be fused, and preferably are not rotationallysymmetrical about their longitudinal axis.

While the exact curvature of a particular vertebral body may not beknown, the teaching of having the implant trailing end be arcuate ortruncated along one side or from side to side so as to eliminate thesize limiting corner or the side wall or lateral aspect junction to theimplant trailing end is of such benefit that minor differences do notdetract from its benefit. Further, the range of describable curvaturesmay be varied proportionately with the size of the implants as well astheir intended location within the spine and direction of insertion tobe most appropriate and easily determinable by those of ordinary skillin the art.

Generally in the lumbar spine, the arc of radius of the curvature shouldbe from 15 to 30 millimeters to be of greatest benefit, though it couldbe greater or less, and still be beneficial. The same is true for thecervical spine where the arc of radius is 10-30 mm, with 15-20 mm beingpreferred. Similarly, the trailing end could be curved at least in part,but not be an arc of a circle and still practice the present invention.

With reference to FIGS. 15A and 15B, as a substitute for contouring theentire trailing end, the trailing end may have a configuration that maybe straight across and then chamfered as illustrated by implant 200 orradiused to one side only as illustrated by implant 800, sufficient toeliminate what would otherwise be a protruding corner when said implantwould be properly inserted and as previously described both lateral wallrear end junctions could be chamfered or radiused.

The implants of the present invention can be configured to have amaximum distance from a horizontal plane HP perpendicular to andbisecting a length along the mid-longitudinal axis MLA of the implantand the trailing end of the implant that is greater than the distancefrom the horizontal perpendicular plane HP to the trailing end of atleast one of the opposite side walls of the implant. This maximumdistance may be greater than the distance from the perpendicular planeHP to the trailing end of both of the side walls, or the distance fromthe perpendicular plane HP to the trailing end of the second side wallcan be greater than the distance from the perpendicular plane HP to thetrailing end of the first side wall. Alternatively, the distance fromthe perpendicular plane to the trailing end of the second side wall canbe greater than the distance along the mid-longitudinal axis from theperpendicular plane HP to the trailing end and greater than the distancefrom the perpendicular plane HP to the trailing end of the first sidewall. The implants of the present invention may also have a maximumfirst length L measured along a first implant side wall that is longerthan a second maximum length S measured along a second implant sidewall.

As should be evident from the above discussion, all of these embodimentsallow for an interbody spinal fusion implant utilizing an element ofrotation for the proper insertion of the implants having at least onerelieved or foreshortened aspect of at least one sidewall to endjunction for placement laterally so as to not protrude unsafety from thedisc space.

As per FIGS. 16A and 16B, it should be appreciated then that a top viewof the trailing end must have a convex type profile as illustrated byimplant 900 while the side view will not or to a much lesser extent.That is, the trailing end of the present invention implants arerotationally asymmetrical about the mid-longitudinal axis MLA even whensymmetrical from side to side, which side to side symmetrically is not arequirement of the broad inventive concept of the present invention. Tohave the opposed vertebrae engaging surfaces protrude dangerously beyondthe perimeter of the disc space so as to impinge on the blood vessels orother vital structures proximate the spine is absolutely contrary to theteachings of the present invention which teaches a safe means forallowing the optimal sizing of the implant(s). As shown in FIG. 16B, thelong sides “L” of implants 700-900 are generally the same.

While the present invention has been taught using implants requiringrotation for their insertion, this has been done to highlight that thepresent invention is counterintuitive and non-obvious. The additionalimplant length made possible by the present inventive teaching actuallyprovides for an implant that would seem to in all but the final selectedposition protrude dangerously from the spine. And indeed it would exceptthat all implants require at a minimum a clear path for their insertion.Thus, while the extended trailing portion does extend from the spineuntil its final rotation into correct alignment it does so when thevital structures, organs, vessels, etc., are retracted and protected andceases to do so thereafter when those structures are released back totheir normal positions in relationship to the spine.

Thus, while the present invention has been explained in regard to suchimplants requiring rotation for their insertion, the present inventionis not so limited and is useful for all interbody spinal fusion implantshaving opposed arcuate upper and lower surfaces or surface portions forpenetrable engagement into the bodies of vertebrae adjacent a disc spaceto be implanted. Moreover, such implants may include at least oneopening therethrough to allow for the growth of bone from vertebral bodyto vertebral body and through the implant.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from thisinvention in its broader aspects and, therefore, the aim in the appendedclaims is to cover all such changes and modifications as fall within thetrue spirit and scope of this invention.

While specific innovative features may have been presented in referenceto specific examples, they are just examples, and it should beunderstood that various combinations of these innovative features beyondthose specifically shown are taught such that they may now be easilyalternatively combined and are hereby anticipated and claimed.

The invention claimed is:
 1. A manufactured preformed interbody spinalfusion implant for insertion at least in part across a surgicallycorrected height of a disc space between two adjacent vertebral bodiesof a human spine, the vertebral bodies having an anterior aspect, aposterior aspect, and to each side a lateral aspect, said implantcomprising: a leading end for insertion into the disc space, an oppositetrailing end, a lateral side and an opposite medial side, said sidesconnecting said leading and trailing ends, said implant having a lengthbetween said leading end and said trailing end and a maximum width asmeasured from said lateral side to said medial side transverse to thelength of said implant; opposed arcuate portions adapted for placementtoward and into the adjacent vertebral bodies, said implant having amaximum height between said opposed arcuate portions defining an implantmaximum height greater than the surgically corrected height of the discspace into which said implant is to be implanted, the maximum height ofsaid implant being transverse to the maximum width of said implant, saidopposed arcuate portions each extending from said lateral side to saidmedial side along the maximum width of said implant; and amid-longitudinal axis passing through said leading and trailing ends,the mid-longitudinal axis being perpendicular to and bisecting each ofthe maximum height and the maximum width of said implant into equalparts, said opposed arcuate portions each including a convex portionacross the mid-longitudinal axis of said implant in a plane transverseto the mid-longitudinal axis of said implant, said opposed arcuateportions forming part of the same circle, the circle having a diametersubstantially equal to said implant maximum height, each of said opposedarcuate portions having at least one opening, said openings being incommunication with one another to permit for the growth of bone fromadjacent vertebral body to adjacent vertebral body through said implant,said trailing end having an exterior surface, a majority of saidexterior surface being linear from one of said opposed arcuate portionsto the other of said opposed arcuate portions across the maximum heightof said implant, said trailing end including a curved portion in a planeparallel to the mid-longitudinal axis of said implant, said curvedportion extending from said medial side and across the mid-longitudinalaxis of said implant, said curved portion adapted to conform to theperipheral contour of the vertebral bodies adjacent the disc space inwhich said implant is implanted, the length of said implant havingbetween said leading end and said trailing end adapted to permit atleast a portion of said implant proximate said trailing end and at leasta portion of said implant proximate said leading end between said medialside and the mid-longitudinal axis to each overlie at least theapophyseal rim of the adjacent vertebral bodies when said implant isimplanted in the disc space, said implant having a junction of saidlateral side and said leading end and a junction of said lateral sideand said trailing end not substantially protruding from the vertebralbodies when implanted in the disc space.
 2. The implant of claim 1,wherein said implant includes a maximum length and a minimum length,said minimum length being located along one of said sides.
 3. Theimplant of claim 1, further comprising at least one protrusion extendingfrom at least one of said opposed arcuate portions for engaging at leastone of the adjacent vertebral bodies to maintain said implant within thedisc space.
 4. The implant of claim 3, wherein said protrusion comprisesa thread for engaging each of the adjacent vertebral bodies.
 5. Theimplant of claim 4, wherein said thread is continuous and uninterrupted.6. The implant of claim 3, wherein said protrusion comprises a ridge. 7.The implant of claim 1, further comprising a plurality of surfaceroughenings for engaging the adjacent vertebral bodies and formaintaining said implant in place, said surface roughenings beingpresent on at least a portion of said opposed arcuate portions.
 8. Theimplant of claim 1, wherein each of said opposed arcuate portionscomprises an interior surface, said interior surfaces being spaced apartto define a hollow interior in communication with said openings.
 9. Theimplant of claim 1, wherein said opposed arcuate portions have a poroussurface.
 10. The implant of claim 1, wherein said implant is formed of amaterial other than bone.
 11. The implant of claim 10, wherein saidimplant material is selected from the group consisting of surgicalquality titanium and its alloys, cobalt chrome alloy, tantalum, anymetal or alloy suitable for the intended purpose, any ceramic materialsuitable for the intended purpose, any plastic or composite materialsuitable for the intended purpose.
 12. The implant of claim 1, whereinat least a portion of said leading end is tapered for facilitatinginsertion of the implant between the two adjacent vertebral bodies. 13.The implant of claim 1, wherein said opposed arcuate portions are in adiverging relationship at least in part to each other for allowingangulation of the adjacent vertebral bodies relative to each other. 14.The implant of claim 1, wherein said opposed arcuate portions aregenerally in a converging relationship from the trailing end to theleading end to each other for allowing angulation of the adjacentvertebral bodies relative to each other.
 15. The implant of claim 1,wherein said implant is configured to require an element of rotation forproper insertion.
 16. The implant of claim 1, wherein at least a portionof said implant is bioresorbable.
 17. The implant of claim 1, incombination with an osteogenic material.
 18. The implant of claim 17,wherein said osteogenic material includes at least one of bone, coral,bone morphogenetic protein, and genes coding for the production of bone.19. The implant of claim 1, in combination with an instrument forinserting said implant at least in part into the disc space.
 20. Theimplant of claim 1, wherein the maximum height is substantially equal tothe maximum width.
 21. The implant of claim 1, wherein each of saidopposed arcuate portions include a plurality of openings.
 22. Theimplant of claim 1, wherein at least a portion of said trailing endextends a distance further rearward on one side of the mid-longitudinalaxis than another side of the mid-longitudinal axis relative to thefirst plane.
 23. The implant of claim 1, further comprising a thread forengaging each of the adjacent vertebral bodies, a portion of said threadbeing located a distance from said leading end greater than the lengthof one of said sides.
 24. The implant of claim 1, wherein said leadingend is curved from side to side across the width of said implant. 25.The implant of claim 24, wherein said leading end has a radius ofcurvature that is different from a radius of curvature of said curvedportion of said trailing end.
 26. The implant of claim 1, wherein saidlateral side has a maximum length and said medial side has a maximumlength greater than the maximum length of said lateral side.
 27. Theimplant of claim 1, wherein said curved portion of said trailing end ofsaid implant is non-threaded.
 28. The implant of claim 1, wherein saidopposed arcuate portions and said sides form a unitary structure. 29.The implant of claim 1, wherein said leading end includes a curvedportion in a plane parallel to the mid-longitudinal axis of said implantextending from said medial side and across the mid-longitudinal axis ofsaid implant.
 30. A manufactured preformed interbody spinal fusionimplant for insertion at least in part across a surgically correctedheight of a disc space between two adjacent vertebral bodies of a humanspine, the vertebral bodies having an anterior aspect, a posterioraspect, and to each side a lateral aspect, said implant comprising: aleading end for insertion into the disc space, an opposite trailing end,a lateral side and an opposite medial side, said sides connecting saidleading and trailing ends, said implant having a length between saidleading end and said trailing end and a maximum width as measured fromsaid lateral side to said medial side transverse to the length of saidimplant; opposed arcuate portions adapted for placement toward and intothe adjacent vertebral bodies, said implant having a maximum heightbetween said opposed arcuate portions defining an implant maximum heightgreater than the surgically corrected height of the disc space intowhich said implant is to be implanted, the maximum height of saidimplant being transverse to the maximum width of said implant, saidopposed arcuate portions each extending from said lateral side to saidmedial side along the maximum width of said implant; and amid-longitudinal axis passing through said leading and trailing ends,the mid-longitudinal axis being perpendicular to and bisecting each ofthe maximum height and the maximum width of said implant into equalparts, said opposed arcuate portions each including a convex portionacross the mid-longitudinal axis of said implant in a plane transverseto the mid-longitudinal axis of said implant, said opposed arcuateportions forming part of the same circle, the circle having a diametersubstantially equal to said implant maximum height, each of said opposedarcuate portions having at least one opening, said openings being incommunication with one another to permit for the growth of bone fromadjacent vertebral body to adjacent vertebral body through said implant,said trailing end being asymmetrical in a cross sectional planetransverse to the mid-longitudinal axis, said trailing end having anouter perimeter that curves at least in part along a plane transverse tothe mid-longitudinal axis, said trailing end including a curved portionin a plane parallel to the mid-longitudinal axis of said implant, saidcurved portion extending from said medial side and across themid-longitudinal axis of said implant, said curved portion adapted toconform to the peripheral contour of the vertebral bodies adjacent thedisc space in which said implant is implanted, the length of saidimplant between said leading end and said trailing end adapted to permitat least a portion of said implant proximate said trailing end and atleast a portion of said implant proximate said leading end between saidmedial side and the mid-longitudinal axis to each overlie at least theapophyseal rim of the adjacent vertebral bodies when said implant isimplanted in the disc space, said implant having a junction of saidlateral side and said leading end and a junction of said lateral sideand said trailing end not substantially protruding from the vertebralbodies when implanted in the disc space.
 31. The implant of claim 30,wherein said implant has a maximum length and a minimum length, saidminimum length being located along one of said sides.
 32. The implant ofclaim 30, further comprising at least one protrusion extending from atleast one of said opposed arcuate portions for engaging at least one ofthe adjacent vertebral bodies to maintain said implant within the discspace.
 33. The implant of claim 32, wherein said protrusion comprises athread for engaging each of the adjacent vertebral bodies.
 34. Theimplant of claim 33, wherein said thread is continuous anduninterrupted.
 35. The implant of claim 32, wherein said protrusioncomprises a ridge.
 36. The implant of claim 30, further comprising aplurality of surface roughenings for engaging the adjacent vertebralbodies and for maintaining said implant in place, said surfaceroughenings being present on at least a portion of said opposed arcuateportions.
 37. The implant of claim 30, wherein each of said opposedarcuate portions comprises an interior surface, said interior surfacesbeing spaced apart to define a hollow interior in communication withsaid openings.
 38. The implant of claim 30, wherein said opposed arcuateportions have a porous surface.
 39. The implant of claim 30, whereinsaid implant is formed of a material other than bone.
 40. The implant ofclaim 39, wherein said implant material is selected from the groupconsisting of surgical quality titanium and its alloys, cobalt chromealloy, tantalum, any metal or alloy suitable for the intended purpose,any ceramic material suitable for the intended purpose, any plastic orcomposite material suitable for the intended purpose.
 41. The implant ofclaim 30, wherein at least a portion of said leading end is tapered forfacilitating insertion of the implant between the two adjacent vertebralbodies.
 42. The implant of claim 30, wherein said opposed arcuateportions are in a diverging relationship at least in part to each otherfor allowing angulation of the adjacent vertebral bodies relative toeach other.
 43. The implant of claim 30, wherein said opposed arcuateportions are generally in a converging relationship from the trailingend to the leading end to each other for allowing angulation of theadjacent vertebral bodies relative to each other.
 44. The implant ofclaim 30, wherein said implant is configured to require an element ofrotation for proper insertion.
 45. The implant of claim 30, wherein atleast a portion of said implant is bioresorbable.
 46. The implant ofclaim 30, in combination with an osteogenic material.
 47. The implant ofclaim 46, wherein said osteogenic material includes at least one ofbone, coral, bone morphogenetic protein, and genes coding for theproduction of bone.
 48. The implant of claim 30, in combination with aninstrument for inserting said implant at least in part into the discspace.
 49. The implant of claim 30, wherein the maximum height issubstantially equal to the maximum width.
 50. The implant of claim 30,wherein the entire outer perimeter of said trailing end is curved. 51.The implant of claim 30, wherein each of said opposed arcuate portionsinclude a plurality of openings.
 52. The implant of claim 30, wherein atleast a portion of said trailing end extends a distance further rearwardon one side of the mid-longitudinal axis than another side of themid-longitudinal axis relative to a transverse cross sectional planeperpendicular to the mid-longitudinal axis.
 53. The implant of claim 30,further comprising a thread for engaging each of the adjacent vertebralbodies, a portion of said thread being located a distance from saidleading end greater than the length of one of said sides.
 54. Theimplant of claim 30, wherein said leading end is curved from side toside across the width of said implant.
 55. The implant of claim 54,wherein said leading end has a radius of curvature that is differentfrom a radius of curvature of said curved portion of said trailing end.56. The implant of claim 30, wherein said lateral side has a maximumlength and said medial side has a maximum length greater than themaximum length of said lateral side.
 57. The implant of claim 30,wherein said curved portion of said trailing end of said implant isnon-threaded.
 58. The implant of claim 30, wherein said opposed arcuateportions and said sides form a unitary structure.
 59. The implant ofclaim 30, wherein said leading end includes a curved portion in a planeparallel to the mid-longitudinal axis of said implant extending fromsaid medial side and across the mid-longitudinal axis of said implant.